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Section 4.0—Environmental Setting and Discussion ofLnpacts <br />Table 4.12-3. The proposed project does not require pile driving. Therefore, as shown in Table <br />4.12-3, the highest vibration levels could occur during the use of a vibratory roller to compact soil, <br />which are estimated to be approximately 0. 110 PPV and below the 0.3 in/sec PPV threshold. Due to <br />the proposed modular construction process, on-site construction activities would be completed faster <br />than compared to traditional construction techniques and would take approximately five months to <br />complete. The shorter construction period would reduce the duration of construction vibration <br />impacts of the proposed project. For these reasons, the project would not expose people to excessive <br />groundbornc vibration. (Less Than Significant Impact) <br />Table 4.12-3: Construction Vibration Levels <br />Source PPV @ 45 Feet <br />Pile Driver (Impact) <br />Pile Driver (Sonic) <br />Clam Shovel Drop <br />Hydromill (Slurry Wall) <br />Vibratory Roller <br />Hoe Ram <br />Large Bulldozer <br />Caisson Drilling <br />Loaded Trucks <br />Jackhammer <br />Small Bulldozer <br />Upper Range 0.607 <br />Typical 0.337 <br />Upper Range 0.384 <br />Typical 0.089 <br />0.106 <br />In Soil 0.004 <br />In Rock 0.009 <br />0.110 <br />0.047 <br />0.047 <br />0.047 <br />0.040 <br />0.018 <br />0.002 <br />Source: Illingworth & Rodkin, Inc. Acoustics and Air Quality. <br />Operational Noise Impacts <br />Once construction is complete, noise levels generated by school operations, including outdoor <br />activities such as recess and physical education, would be similar to existing conditions. With the <br />project, no new noise sources are proposed; there would just be more students participating in the <br />existing school activities. In order to have a perceptible (3 dB) increase in ambient noise levels, all <br />noise sources must double. If noise sources are increased by 50%, there is a 2 dB increase in noise <br />levels, and if noise sources increase by 25%, there is a one (1) dB increase in noise level .29 The <br />project would increase school capacity by 220 students, or approximately 40%. Noise caused by <br />=9 Michael Thill, Rlingivorth & Rodkin, Inc., Noise Consultants, personal communications. October 6, 2016. <br />City of Redwood City 78 Initial Study/Mitigated Negative Declaration <br />Sandpiper Elementary School Facilities Expansion November 2016 <br />